High-temperature polar clusters in perovskite-type relaxor ferroelectrics and their response to an electric field

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Relaxor ferroelectrics are locally inhomogeneous materials that have been attracted tremendous attention due to their exceptional dielectric, electromechanical and electrooptic response. The unique relaxor properties are related to the existence of polar nanoclusters dispersed in the overall cubic structure. The understanding of the actual polar atomic clustering and its interplay with the relaxor properties is a great challenge to condensed-matter physicists and materials scientists. This project aims to analyze the preferential polar atomic shifts and coupling processes to form polar nanoregions at temperatures above the temperature of the dielectric permittivity maximum. For the purpose, resonance Raman spectroscopy will be applied to model compounds (stoichiometric and Ba-doped PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3) in the temperature range 670 – 80 K to analyze the evolution of the mean size and distribution of polar species via the changes in the enhanced longitudinal optical modes. Further, the same compounds will be studied by in situ conventional Raman spectroscopy under an external electric field at temperatures between 850 and 80 K to elucidate the preferred crystallographic direction of coherent polar atomic displacements and the switchability of polar clusters. In addition, the temperature evolution of phonon and valence-electron states of newly synthesized Ru-containing PbSc0.5Ta0.5O3, PbSc0.5Nb0.5O3 and 0.9PbZn1/3Nb2/3O3-PbTiO3 will be analyzed by Raman spectroscopy and optical ellipsometry.